The present invention relates to a method and device for storing data so that it is strengthened against bit errors produced in memory cells by dispersing the stored data in a memory device so as to be suitable for use in an environment, where radiation conditions are bad, such as space, nuclear reactors, etc. It relates further to a data dispersion type memory method suitable for a work memory for image or aural data, etc., in which the amount of the data that is accessed only a relatively small number of times, is reduced so that the memory area for new input data is secured automatically.
Of this kind of prior art memory devices, there is known a semiconductor memory device disclosed e.g. in Journal of Electronic Communication Society of Japan (in Japanese), Vol. 67, No. 11, pp. 1134-1145 (1984). In this device, as indicated in FIG. 1, one input data set (write-in information) 14 is stored in a memory cell 16 in the memory device, i.e. in a memory cell matrix 13 selected by an address information 10, an address register 11 and a decoder 12 with a one-to-one relation. A retrieved data set (read-out information) 15 is, similarly to the storing, retrieved from a memory cell 16 in the memory cell matrix 13 selected by the address information 10, the address register 11 and the decoder 12.
The prior art memory device described above has the problem that since the stored input data and the memory place are in a one-to-one relation, in the case where information stored in a specified memory cell is destroyed by influences of radiation, etc., it is impossible to restore the information.
Further such a prior art memory device has another problem that since no attention is paid to the frequency of use of the stored data, when the amount of the stored data reaches the limit of the memory capacity, a part of the data could be erased artificially. For solving this problem a proposal has been made of an autonomous resources management system with recorded evolutions of system performance with scheduler control including a knowledge learning function in a computer system in JP-A-Sho 60-24647. By this method job management data is utilized for utilizing efficiently resources of the computer system. It is necessary therefor to store management data generated time-sequentially to manage the system efficiently.
By this method it is proposed that when new job management data different from the stored job management data is generated, all information of the data stored in an old data storing region is erased, depending on the frequency of use of the stored data, in order to secure an input data area, and new data is stored in the storing region stated above.
However the method described above has still another problem that no attention is paid to the case where a renewed retrieval is required for the data once erased.
That is, the prior art techniques described above have serious problems that;
(1) it is difficult to retrieve and restore deficient data, and PA1 (2) data occupies the memory capacity, independently of the importance thereof. PA1 (1) Even in the case where a part of data in the storing portion is destroyed by external perturbation, since data is stored dispersedly, it is possible to restore it by executing a convolution operation thereof with a predetermined retrieval function. PA1 (2) Although the amount of data, for which the relative number of accesses is small, is reduced (forgotten), since that data is stored dispersedly, even if the amount of data is reduced in some degree, it can be restored and retrieved. Due to this partially forgetting function, the amount of data is reduced automatically and a new data storing area is secured. In this way the memory device is never unable to write-in new data and it is possible to manage efficiently the memory device.